Changes between Version 7 and Version 8 of FAQ

Timestamp:

Apr 17, 2009, 6:38:21 PM (15 years ago)

Author:

mloskot

Comment:

FAQ: How to write geometry Well-Known-Binary to hex-encoded string?

FAQ

@@ -5 +5 @@
 [[TOC(depth=2, noheading, inline)]]
 
-== How to create geometry from hex-encoded WKB using SQL? ==
+== How to create geometry from hex-encoded Well-Known-Binary string using SQL? ==
 
-This is two-steps operation which can be executed in single SQL statement. The steps include:
- 1. Convert WKB data in hexadecimal string form to raw binary using PostgreSQL function [http://www.postgresql.org/docs/8.3/static/functions-binarystring.html decode].
- 2. Construct geometry object from WKB in raw binary form.
+This is two-steps operation which can be executed in single [http://www.postgresql.org/docs/8.3/static/sql-commands.html SQL] statement. The steps include:
+ * Convert [http://postgis.refractions.net/documentation/manual-svn/ch04.html Well-Known-Binary] data in hexadecimal string form to raw binary using PostgreSQL function [http://www.postgresql.org/docs/8.3/static/functions-binarystring.html decode].
+ * Construct geometry object from WKB in raw binary form.
 
 Example:
@@ -15 +15 @@
 {{{
 #!sql
-=# SELECT ST_AsText(ST_GeomFromWKB(decode('0101000000e5d022dbf93e2e40dbf97e6abc743540', 'hex'), 4326));
+=# SELECT ST_AsText(ST_GeomFromWKB(decode('0101000000e5d022dbf93e2e40dbf97e6abc743540', 'hex'), -1));
       st_astext       
 ----------------------
  POINT(15.123 21.456)
 }}}
+
+== How to write geometry Well-Known-Binary to hex-encoded string? ==
+
+First, query for geometry object in [http://postgis.refractions.net/documentation/manual-svn/ch04.html Well-Known-Binary] format using [http://postgis.refractions.net/documentation/manual-svn/ST_AsBinary.html ST_AsBinary] function. Then, [http://www.postgresql.org/docs/8.3/static/functions-binarystring.html encode] raw WKB to hex string.
+
+Examples:
+
+ * selecting geometry from table:
+
+{{{
+#!sql
+# SELECT encode(ST_AsBinary(the_geom), 'hex');
+                   encode                   
+--------------------------------------------
+ 0101000000e5d022dbf93e2e40dbf97e6abc743540
+}}}
+
+ * constructing geometry in-place from given Well-Known-Text:
+
+{{{
+#!sql
+# SELECT encode(ST_AsBinary(ST_GeomFromText('POINT(15.123 21.456)', -1)), 'hex');
+                   encode                   
+--------------------------------------------
+ 0101000000e5d022dbf93e2e40dbf97e6abc743540
+}}}